# Climbing stairs

##### Class practical

Estimating the energy transferred to potential energy in climbing a flight of stairs.

#### Apparatus and materials

Bathroom scales

Tape measure, 5 m

#### Health & Safety and Technical notes

Since this activity does not require the time taken to be measured, a delegation could measure the height while the class remains in the laboratory or classroom.

#### Procedure

a Each student must know their mass in kilograms, or use the scales to determine it.

b Measure the height of the stairs from the ground floor to the top of the highest step.

c Each student climbs the flight of stairs and calculates the increase in their gravitational store of energy.

#### Teaching notes

1 When someone climbs the stairs energy is transferred from the chemical store of energy in their muscles (food and oxygen) to increase their gravitational potential energy. Gravitational potential energy = mgh.

Where mg is the weight of the climber and h is the vertical distance climbed.

2 You may need skills in crowd control if other classes are not to be disturbed and students are not to get hurt. Students may try to turn this experiment into a demonstration of power, by timing how fast they can get to the top of the stairs!

3 Students may also ask why they feel fatigued when they hold up a load but the load doesn't move. In order to grip the load, muscles are kept tensed; they squeeze the blood vessels and restrict blood flow. As a result the chemical products of muscular activity accumulate and are not washed away so quickly by the blood. This accumulation of chemical products makes the nerves give a sense of fatigue. So the feeling of fatigue is chiefly an indirect result of the muscle tension.

The continuing demand on chemical energy while you hold a load at rest arises from the muscle fibres developing tension very rapidly, drawing on chemical energy. In a large muscle, fibre after fibre is fired into tension as a nerve impulse arrives but each fibre soon relaxes. Later on it renews its tension again. When the fibre is released the energy is transferred only to thermal energy and not to the energy stored in chemicals. So the steady pull of a muscle is really the result of many brief tugs, a dynamic force. The sum total of these pulses of force shows tiny statistical fluctuations like a trembling effect.

This experiment was safety-checked in January 2006